Cathodic Protection System for Water Heaters with Sealant

ABSTRACT

A cathodically protected lined water heater tank in which zinc rich paint is employed between the tank of the water heater and fittings, threaded or otherwise secured to the tank. The zinc rich paint acts as a distributed or secondary anode to charge exposed metal at the location of the paint with a protective potential against corrosion and also as a sealant which increases in volume for increased sealing effect when products of corrosion are produced as the zinc rich paint reacts with the water in the water heater. The zinc rich paint is used in combination with a primary zinc anode extending within the fluid stored in the water heater.

United States Patent Wasson 1 Feb. 4, 1975 [54] CATHODIC PROTECTION SYSTEM FOR 2,423,290 7/1947 Bonwitt 204/197 WATER RS I SEALANT 5,359,123 1/1949 Bates et al. 1 1 204/197 41,935 6/1960 Miller et al. 204/197 Inventor: Lqerwflod wasson, Mllwaukee, 3,332,867 7/1967 Miller et al. 204/197 WIS. 3,354,063 11/1967 Shutt 204/148 [73] Assignee: A. O. Smith Corporation,

Milwaukee, Primary ExammerT. Tung l Attorney, Agent, or Firm-Andrus. Sceales. Starke & Flledi May 8, Sawall [2]] Appl. No.: 358,369

[57] ABSTRACT U S A cathodically protected lined Water heater tank in 285/55 285/192 403/288 which zinc rich paint is employed between the tank of 403/410220/46 the water heater and fittings, threaded or otherwise [51] Int Cl (123i 13/00 F24h H00 F24h H20 secured to the tank. The zinc rich paint acts as a dis- [58] Field "s'; 504/148 219/312 tributed or secondary anode to charge exposed metal 219/322. 285/55 403/288 at the location of the paint with a protective potential against corrosion and also as a sealant which increases in volume for increased sealing effect when products fcorrosion are produced as the zinc rich paint reacts [56] References Cited with the water in the water heater. The zmc rich paint UNITED STATES PATENTS is used in combination with a primary zinc anode ex- M111S tending the tored in the water heater 5 Claims, 2 Drawing Figures CATIIODIC PROTECTION SYSTEM FOR WATER HEATERS WITH SEALANT BACKGROUND OF THE INVENTION lt has been customary to use a common pipe dope as sealing material for openings in water heater tanks into which it is necessary to dispose fittings. This common pipe dope is of high viscosity consisting usually of an inert filler mixed into a convenient carrier and which does not solidify in service but rather maintains its flowable characteristics. The present invention uses a zinc-rich paint as the joint sealant which solidifies within the joint in which it is located. The paint has fine particles of solid zinc which act as a distributed or secondary anode to charge exposed metal at the location of the paint with a protective potential against corrosion.

SUMMARY OF THE INVENTION The invention is directed to the cathodic protection system for storage tanks which makes it possible with a sealant of an anodic material to seal the joints between fittings secured to the tank which sealant becomes more effective with the passage of time and at the same time develops a protective potential in the respective joints even in the presence of high resistivity waters. It has been found that when the exposed metal in the joints between fittings has been charged by anodic material, it is then possible to prevent corrosion of such metal with a potential level which is less anodic than the one which is required to achieve the original protective level.

The invention is particularly directed to the cathodic protection of water heater tanks which are glass coated on the inside to protect the metal of the tank from corrosion by the water contained within the tank. It is common to use magnesium anodes in water heaters to cathodically protect metal of the tank which may be exposed through the glass lining or at fittings to the water stored in the tank. Magnesium anodes may be used as the primary anode with the invention but the invention makes it possible to satisfactorily use the less expensive zinc anodes.

The system besides the primary anode includes a secondary anode of the distributed type in that it is provided by zinc rich paint disposed as a sealant in the joints between openings in the tank wall and each respective fitting. The zinc rich paint is in mechanical contact with the metal at the fitting joints whether the fitting be threaded into the wall of the tank or otherwise secured thereto. The zinc rich paint provides cathodic protection of the metal in the fitting joints at the start of operation of the heater. In addition, the zinc rich paint charges the exposed metal at the fitting joints in such a way that the metal thereafter maintains its corrosion immunity with much less protective potential than is required to create such immunity. This permits the use of the lower potential zinc primary anode which is of advantage, particularly in water where a magnesium anode sometimes causes the presence of deleterious odors.

The zinc rich paint used as the joint sealant and distributed anode is a combination of a carrier plus fine particles of solid zinc which has particular advantage when employed as a joint sealant. The zinc particles in the paint react with the water in the heater and will tend to corrode. The corrosion products of the zinc metal occupy more volume than the zinc metal itself, and consequently will act to seal the fitting joints. Therefore, the seal of the joints between the respective fittings and tank wall will become tighter with the passage of time.

DESCRlPTION OF THE DRAWING FIGURES The drawings furnished herewith illustrate the best mode of the invention presently contemplated by the inventor for carrying out the practice of the invention.

ln-the drawings:

FIG. 1 is a longitudinal sectional view of a water heater with parts in elevation, in perspective and shown diagrammatically; and

FIG. 2 is an enlarged view of the joint between the heating element fitting and tank wall such as is employed in an electric water heater.

Referring to the drawing, there is shown a water heater tank 1 which has stored water therein which is heated by the gas burner 2 actuated by the thermostat 3, the connections therebetween not being shown. The tank 1 includes a shell 4 and the outwardly extending upper head 5 and the inwardly dished lower head 6. A flue 7 extends centrally of tank 1 to carry off the products of combustion produced by gas burner 2. The inside of tank 1 and flue 7 is coated with glass or ceramic 8 to protect the metal of the tank and flue from corrosion by the water stored therein.

FIG. 1 of the drawing also illustrates a zinc anode 9 which is supported from an outlet fitting 10 having an outlet therein and which is threaded within an opening in the upper head 5. The anode 9 extends within tank 1 to adjacent the lower head 6. Anode 9 is anodic to the metal of tank 1 and affords corrosion protection to any metal of tank 1 exposed through lining 8 or metal of the fittings employed in the tank such as outlet fitting 10. The anode 9 preferably is of zinc and may be otherwise secured within the tank 1 than being suspended from the outlet fitting l0. Corrosion protection of exposed metal within tank 1 is accomplished by electrolytic action in the water stored in the tank occurring between the anode 9 and exposed metal.

Besides outlet fitting 10 the tank 1 is provided with an inlet pipe 11 which is supported from inlet fitting 12 in turn threaded into another opening in head 5. lnlet pipe 11 extends to adjacent the bottom of tank 1. The drain cock fitting 13 for draining water from tank 1 is threaded into an opening in the lower portion of shell 4 of tank 1. Furthermore, the thermostat fitting 3 is shown diagrammatically as threaded into an opening in shell 4 at a position above drain cock 13. The described fittings result in the threaded joints 14 between the respective fittings and the fitting element openings in the wall of tank 1.

In the joint 14 between each of the described fittings l0, l2, l3 and 3 and the respective fitting element openings in tank 1 within which the fittings are threaded, there is provided a sealant 15 which preferably is of a zinc rich paint. In any event the sealant material employed must contain a metal which is anodic to the steel of tank 1 such as zinc, aluminum or magnesium so that sealant 15 operates not only as a sealant but also as a secondary or distributed anode.

The zinc rich paint which is preferably employed as sealant 15 consists of a carrier such as ethyl silicate and fine particles of solid zinc of a grain size such as, for example, of a size to pass through a 300 mesh sieve. The

zinc rich paint solidifies so that it will not be pushed out of joints 14 under the pressures to which it might be subjected.

The electrical contact between the sealant 15 and any bare metal exposed in joints 14 is accomplished by mechanical contact with the bare metal. The zinc rich paint sealant 15, because of the close contact with the metal in joints 14, provides cathodic protection at the metal area of the joints 14 particularly at the commencement of operation of the heater. The protection of the metal area of joints 14 by the secondary or distributed anode sealant 15 will continue for a sufficient length of time to charge the metal at the joints 14 to a point of corrosion immunity. When the zinc particles in sealant 15 have all been used up, the primary anode 9 will function to maintain the corrosion immunity, even though the potential developed at the joints 14 by primary anode 9 would not be sufficient to provide corrosion protection if the heater were started in operation without the presence of the distributed anode and sealant 15.

The presence of the paint sealant 15 in the joints 14 creates a potential distribution pattern within the heater, which acts to make the primary anode 9, do a better job of protection of other bare metal in tank 1, because it changes the anode-cathode geometric spacing relationship within the tank in such a way as to enable more protection potential to be established at other metal surfaces which may be exposed to the fluid stored in tank 1.

The sealant 15 of the invention has another effect which is involved with the anodic protective action of the zinc rich paint preferably employed as the sealant. The zinc particles disposed in the sealant l react with the water or fluid stored in tank 1 and tend to corrode. The corrosion products of the zinc metal occupy more volume than the zinc paint itself, and consequently they will act to seal joints 14 more tightly. Therefore, with the passage of time the seal at joints 14 will become even more effective.

HO. 2 illustrates the connection of an electric heating element fitting 16 to the shell 17 of an electric water heater to illustrate a fitting which is not of the threaded type. The element opening 18in the shell 17 is encircled by a mounting bracket 19 which is welded to the outside of shell 17. The heating element 16 is supported on flat plate 20 and extends through opening 18 in shell 17 to the inside of the heater. The flat plate 20 is bolted to mounting bracket 19. The sealing gasket 21 is located between the shell 17 and flat plate 20 to the inside of mounting bracket 19. The zinc rich paint sealant 22 is disposed in opening 18 and in the joint between shell 17, sealing gasket 21 and the mounting bracket 19. The shell 17 is lined on the inside with a corrosion protective glass coating 23.

ln establishing the system of the invention, with respect to FIG. 1 by way of example, after the shell, heads and flue of tank 1 have been welded together with glass lining 8 in place and the described threaded fitting openings provided in their respective locations in tank 1. The fittings l0, l2, l3 and 3 are coated with the anodic sealant and threaded home in their respective openings. In the case of an electric water heater, the heating element fitting 16 of which is shown in FIG. 2, the assembly of the heater follows substantially that described with the gas water heater. However, the mounting bracket 19 is welded to shell 17 before assembly of the heads and shell. After the shell and heads are secured together, the anodic sealant 22 is applied to the heating element opening in the shell 17 and over the outer surface of the shell 17 and the inner end surface of bracket 19. Thereafter, gasket 21 is located over the sealant 22 and flat plate 20 carrying heating element fitting 16 and is bolted to bracket 19.

The invention provides the combination of a primary anode and asecondary anode preferably of distributed zinc rich paint, which provides the required protective potential in the joints between the fittings and the heater tank where the primary anode would be overtaxed to build up corrosion immunity in such areas. Under the invention, the potential of the primary anode is availableto protect other exposed metal of the. tank and has a greater capacity to do so. Furthermore, a primary anode such as of zinc with less potential than magnesium can be employed in most installations. ln addition, the zinc rich paint is a sealant at the fitting joints wherein the zinc particles in the paint over a passage of time corrode away to produce products of corrosion in the sealant which increase the sealant in volume and the effectiveness of the seal.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regardedas the invention.

1 claim:

1. A substantially closed metal tank having a lining disposed on the inside of the tank of a material to protect the metal of the tank from corrosion by the fluid stored within the tank, but leaving some bare metal exposed to said fluid throughout various areas of the tank,

a primary anode more anodic than the exposed metal of thettank and secured to the tank and extending therein in contact with the fluid stored in said tank to cathodically protect the exposed bare metal in the tank, a plurality of fittings secured within openings in the metal tank and forming joints with the tank at said openings in which bare metal may be exposed to the fluid in the tank, and a sealant separate from said fittings disposed in said joints and covering the exposed metal of the tank at the joint area and having particles of metallic material therein more anodic than the metal of the tank distributed throughout said joints, said sealant expanding in volume as products of corrosion are produced in the joints from said particles by contact with the fluid in the tank to increase the sealing effect of the sealant and acting as a secondary distributed anode to cathodically protect the exposed metal in the joints and initially charge any exposed metal in the joints so that less potential is later required to be developed in the joints by the primary anode to provide corrosion protection in the event the distributed anode is used up.

2. The cathodically protected tank of claim 1, in which the sealant material is a zinc rich paint having fine particles of solid zinc of an approximate size to pass through a 300 mesh sieve.

3. The cathodically protected tank of claim 2 in which the primary anode is of zinc.

4. The cathodically protected tank of claim 1 in which some of the fittings are threaded into the tank wall.

5. The cathodically protected tank of claim 1 in which some of the fittings are bolted to the tank wall. il l 

2. The cathodically protected tank of claim 1, in which the sealant material is a zinc rich paint having fine particles of solid zinc of an approximate size to pass through a 300 mesh sieve.
 3. The cathodically protected tank of claim 2 in which the primary anode is of zinc.
 4. The cathodically protected tank of claim 1 in which some of the fittings are threaded into the tank wall.
 5. The cathodically protected tank of claim 1 in which some of the fittings are bolted to the tank wall. 